Answer
$-2\sqrt{7}$
Work Step by Step
Simplify each radical, when needed, to have:
$=3\sqrt{4(7)}-4\sqrt{9(7)} + \sqrt{16(7)}
\\=3 \cdot 2\sqrt{7} -4\cdot3\sqrt{7} + 4\sqrt{7}
\\=6\sqrt{7}-12\sqrt{7} + 4\sqrt{7}$
Combine like terms to have:
$=(6-12+4)\sqrt{7}
\\=-2\sqrt{7}$
